Depending on the cause, your condition may be diagnosed and/or monitored using other tests such as calcium, phosphorus, parathyroid hormone, vitamin D, or bone markers (a group of tests used to measure bone formation and bone resorption).
Because the flu vaccine is produced by private manufacturers, its availability depends on when production is completed. For the 2015-2016 flu season, manufacturers have indicated shipments are likely to begin in July or August and continue throughout September and October until all vaccine is distributed. Doctors and nurses are encouraged to begin vaccinating people as soon as flu vaccine is available in their areas.
You can get a flu vaccine well into flu season, but it's best to try to get it as early as possible so the body has time to build up immunity. However, even in January there are still a few months left in the flu season, so it's still a good idea to get protection.